1. Field of the Invention
This invention relates to a low-voltage type igniter plug having semi-conductor structure for use in jet and other internal combustion engines in which the semi-conductor structure is particularly improved.
In jet engine igniters, an electrically semi-conducting material is mounted within a spark gap between firing-tip of a center electrode and a ground electrode. The semi-conducting material allows for limited current flow to occur along the surface of the semi-conducting material upon application of a low voltage, the current flow causes the requisite ionization and enables a high energy spark discharge with the low applied voltage.
Various semi-conducting materials have heretofore been introduced, and extensively used in igniters fired by low-voltage, high-energy ignition systems.
One example of the semi-conducting materials was disclosed in the specification of U.S Pat. No. 3,558,959 filed Apr. 24, 1968 as continuation-in-part, and patented Jan. 26, 1971.
According to the publication of U.S. Pat. No. 3,558,959, a ceramic semi-conductor body is hot-pressed with silicon carbIde (SiC) and alumina (A1.sub.2 0.sub.3) as essential components which is found to be adequate under severe service condition, in particular high combustion zone temperatures and fuel wetted condition encountered in many those day engines.
In recent years, however, it is demanded for the igniter plug to normally function under a high pressure such as, for example, 20Kg/cm.sup.2 for the purpose of safety.
Under such circumstances, there is possibility that no small amount of erosion will occur even in the semiconductor body carried by U.S. Pat. No. 3,558,959.
Therefore, it is an object of this invention to provide a low-voltage type igniter plug having semi-conductor structure improved to have significantly long service lives when assembled to provide a semi-conductor surface along which a high energy spark discharge occurs in a low voltage under the high pressure.
According to the present invention, there is provided a low-voltage type igniter plug having semi-conductor structure comprising; a center electrode having a firing-tip mounted within a tubular insulator which in turn are placed within an interior of a metallic shell; a ground electrode being electrically contact with the metallic shell and in spaced, a spark-gap relationship with the firingtip of the center electrode; an electrically semi-conducting body, surface of which is mounted adjacent the spark-gap in electrically contact with both the center and ground electrodes; the improvement in which the semi-conducting body essentially consisting of silicon carbide particles less than 5 microns in average diameter, and alumina particles less than 1 micron in average diameter, the weight percent of the silicon carbide particles ranging from 65 to 80 inclusive, the weight percent of the alumina particles ranging from 20 to 35 inclusive, the silicon carbide particles and the alumina particles being mixed with an addition of suitable amount of binder means, and sintered by means of hot press at the temperature above 1800 degrees Celsius inclusive, and at the pressure above 200Kg/cm.sup.2 inclusive.
Thus providing a tough-structured conductor body of nearly 1 in theoretic density in which particles are aligned in well-ordered manner with small number of defects, enabling to decrease the amounts of erosion even when the semi-conducting body is exposed to a spark discharge under the high pressure.
Other object and advantages will be apparent with reference to the following specification, attendant claims, and drawings.